1. Field of the Invention
The invention relates to a process and a device for mixing and piping suspensions of different natures and/or compositions in the stable section of a paper machine.
2. Description of Background Information
A process and device for mixing suspensions is known from U.S. Pat. No. 4,477,313 to Andersson, issued Oct. 16, 1984. According to the Andersson patent, the backwater collected in the paper machine is passed into open backwater tanks, and is then fed back to the headbox via mixing pumps provided with a thick stock supply.
If a change in paper type is made on the paper machine, drainage conditions usually change and, thus, the concentration (e.g., solid content) of the backwater (in particular) usually changes. However, in the Andersson patent, due to the high residence time of the backwater in the backwater tank, the concentration in the backwater tank changes only slowly. This means that stable conditions are established very slowly in the backwater cycle. During this adjustment phase, production must often be slowed down to achieve the required paper quality. Consequently, production and quality losses occur.
Another process and device for mixing suspensions is known from the (Published) German Patent Application No. DE 195 09 522 A1, published Sep. 26, 1996. In this document, a stock suspension is fed to a headbox, that is sectioned over the width of the machine, through a plurality of lines feeding stock suspension. The lines feeding stock suspension are connected to a distributor. A portion of the backwater arriving in the drainage region of the paper machine is fed sectionally to the headbox, and is used for basis weight control according to the well-known dilution principle. The remainder of the backwater is passed into a backwater tank, and sent back from the backwater tank into the stock preparation system ("stable section"), although the stable section is not shown in DE 195 09 522 A1.